Generally heat-developable photosensitive materials contain a base or a base precursor to promote development upon heating. More preferably from the standpoint of shelf stability of the photosensitive material a base precursor which liberates basic substances upon thermal decomposition is used.
Examples of typical base precursors are described in British Pat. No. 998,949.
In this connection, preferred base precursors are salts of carboxylic acids and organic bases. Useful carboxylic acids include trichloroacetic acid, and trifluoroacetic acid. Useful bases include guanidine, piperidine, morpholine, p-toluidine, and 2-picoline.
An especially useful carboxylic acid is guanidine-trichloroacetic acid, which is described in U.S. Pat. No. 3,220,846. Japanese Patent Application (OPI) No. 22625/75 describes aldonamides, which decompose at a high temperature to form a base and therefore these may be advantageously used.
However, most of these prior art base precursors take a relatively long period of time to provide images or suffer occurrence of fog. Furthermore, these base precursors are disadvantageous in that they are influenced by air or moisture which causes decomposition that leads to a deterioration of the photographic properties of the photosensitive material or a substantial degradation of shelf stability thereof.